Why are surface mount LEDs recomended pad sizes so small?

[grizedale]

Page 10 of the following LED datasheet (Xlamp XBD LED) shows a recomended footprint for this LED..........

**broken link removed**


...Why is the anode and cathode pads just 0.284mm wide?

Can i make them wider than that?

For when we make up our prototype boards, we dont have reflow machines, so it will help us if the pads "spill" out to the side a little so that we have something to apply the soldering iron too....but those land patterns are just too small.

We have a hot gas gun, but for obvious reasons, we cannot simply gas-gun this led to the pcb like gets done with mosfets, because we would melt the lens of the LED.

 

[FvM]

Suggested PCB footprints are related to an intended assembly method. For prototype production or other special requirements - change them at will.

For single side assembly, simple hot plate soldering should work well with the suggested footprint, I think.

 

[grizedale]

Thanks, i was worrying that maybe if the pads are too big, the pick and place machine may misalign the LED when it places it?

 

[FvM]

Thanks, i was worrying that maybe if the pads are too big, the pick and place machine may misalign the LED when it places it?

Pick and place is performed according to placement data and hasn't to do with footprint shapes. You'll want to validate the correct alignment in visual inspection, but that's a minor aspect of footprint design. The problem is if the part will keep it's position during reflow. Having the three footprint stripes matched with pads of course promotes self alignment. Enlarging the outer pads would still keep the alignment I think. Or enlarging only the small stubs.